Orthopedic splints or casts are used to support body portions, normally limbs, but frequently also portions of the torso such as the rib cage, for immobilizing the underlying body portions and facilitate healing of various parts of the anatomy. Such casts have both medical and veterinary applications.
In the past, a common splint was a plaster cast. They were formed by supplying bandages covered with plaster of paris, immersing the bandages in water immediately prior to their application, and thereafter wrapping the bandages about the body portions in question, say a leg. After the plaster of paris hardens, a rigid cast is formed. Casts often carry weight and are subject to a certain amount of abuse during daily use. They must therefore be relatively thick, in the order of one inch or more. This represents great bulk and weight which has to be carried around by the patient and greatly restricts his mobility. Moreover, plaster of paris is brittle, breaks upon impact, and deteriorates when subjected to moisture. Even though its characteristics are substantially less than one might desire, plaster casts are widely used because of the simplicity with which they can be applied and because they are relatively inexpensive.
Some of the shortcomings experienced with plaster casts were overcome by orthopedic splints made from a plastic webbing or fabric which is wrapped about the leg. The fabric is solidified by first applying a solvent so that surface areas of the fabric are liquefied. After the solvent evaporates, the dissolved fabric material solidifies again and forms a rigid matrix since portions of the fabric loops in contact with each other fuse together. This cast or splint and certain improvements and variations thereof are illustrated and described in U.S. Pat. Nos. 2,308,483; 2,373,802; 2,489,252; and 2,632,442. (hereinafter sometimes referred to as "fabric patents").
As is more fully set forth in U.S. Pat. No. 2,489,252, suitable plastic materials include cellulose plastic such as cellulose esters, cellulose ethers; polystyrene plastics; and vinyl ester plastics such as polyvinyl acetate, polyvinyl chloride, polyvinyl chloride acetate and copolymers of vinyl acetate, and vinyl chloride. Solvents for such materials include ethyl acetate, acetone, methyl acetate, methyl formate, and others.
Another approach utilizing plastic materials as a replacement for plaster casts is the impregnation into a backing web such as a gauze or fabric of a fusible plastic material. The plastic impregnated web is wrapped around the broken limb after which it is heated, molded and cooled to form a relatively rigid cast. As more fully described in the U.S. Pat. No. 3,692,023, suitable fusible plastic materials may include blends of cyclic ester polymers such as poly-epsilon-caprolactone and poly-(vinyl alkyl ethers) such as poly-(vinyl ethyl ether). Use of heat fusible materials eliminates the need for solvent activation.
Splints made in this manner are substantial improvements over plaster casts insofar as their overall weight, strength, and moisture resistance is concerned. However, they require relatively expensive raw materials so that such splints are not always as economical as one might desire.
The prior art has also made attempts to improve orthopedic splints by using more lightweight materials such as corrugated cardboard, air inflatable splints or splint sections, and reusable splints. As far as the present invention is concerned, splints employing corrugated materials are the most pertinent. U.S. Pat. Nos. 3,750,660 and 3,656,475 are exemplary. In essence, they show sandwich constructions in which an inner and an outer sheet are separated by a corrugated material having flutes or cells which run essentially parallel to the skin over which the splint is applied. These splints, although of light weight and relatively inexpensive, are primarily temporary splints for field applications. Their strength is very limited, they are normally incapable of resisting moisture, and, on the whole, they are not for permanent use, that is, use for several days up to several months.